The vertebrate spine is the axis of the skeleton providing structural support for the other parts of the body. Adjacent vertebrae of the spine are supported by an intervertebral disc, which serves as a mechanical cushion permitting controlled motion between vertebral segments of the axial skeleton. The intervertebral disc is a unique structure comprised of three components: the nucleus pulposus (“nucleus”), the annulus fibrosus (“annulus”) and two vertebral end plates.
The spinal disc can be displaced or damaged due to trauma, disease, degenerative defects or wear over an extended period of time. For example, disc herniation occurs when annulus fibers are weakened or torn and the inner tissue of the nucleus becomes permanently bulged. The mass of a herniated or “slipped” nucleus tissue can compress a spinal nerve, resulting in leg pain, loss of muscle control, or even paralysis. In addition, in some cases, a degenerated nucleus can lose its water binding ability and deflate, thereby reducing the height of the nucleus and causing the annulus to buckle in certain areas.
To alleviate back pain caused by disc herniation or degeneration, the disc can be removed and replaced by an implant that promotes fusion of the remaining bone anatomy. The implant, such as a spacer or cage body, should be sufficiently strong to support the spine under a wide range of loading conditions. The implant should also be configured so that it is likely to remain in place once it has been positioned in the spine by the surgeon. In addition, the implant should be capable of being delivered minimally invasively or at least through a relatively small incision into a desired position.
Thus, there remains a need for an improved implant that addresses these difficulties.